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Date: Thu, 15 Apr 2010 00:48:25 +0200 From: Krzysztof Halasa <khc@...waw.pl> To: Michael Barkowski <michaelbarkowski@...gedcom.com> Cc: "David S. Miller" <davem@...emloft.net>, Julia Lawall <julia@...u.dk>, "netdev\@vger.kernel.org" <netdev@...r.kernel.org>, "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: hdlc_ppp: why no detach()? Hello Michael, Michael Barkowski <michaelbarkowski@...gedcom.com> writes: > I am looking at your hdlc_ppp code and I don't understand: why is there > not the equivalent of fr_detach() in there? I assume you mean .detach = fr_destroy(). It's used only to kill subdevices, i.e. it has nothing to do with the interface being up/down. > pc8300_drv:cpc_remove_one() frees netdevs quite confidently but I wonder > how it can be so sure that there are not skbs in hdlc_ppp's tx_queue > associated with those devices before freeing them....q Theoretically all paths adding skbs to the tx_queue should send them out before returning (possibly also on behalf of other devices). However I wonder if it's the case. Let's see: Only ppp_tx_cp() adds to the queue directly: - ppp_rx() (calls ppp_tx_flush()) - ppp_timer (calls ppp_tx_flush()) - ppp_cp_event(): - ppp_cp_parse_cr() (calls ppp_tx_flush()) - ppp_stop() calls ppp_cp_event(), but it won't queue any skb, it only marks the connection as closed and does the same to IPCP and IPV6CP. This means the problematic part is ppp_start() which calls ppp_cp_event(LCP, START) = IRC | SCR | 3 meaning Initialize-Restart-Count, Send-Configure-Request and change state to REQ_SENT. This causes two problems: 1. The SCR packet will be delayed by 2 seconds (both first and second SCR will be sent the same time). Perhaps we delay only a little (instead of full 2 seconds) and only then send the initial packet. 2. (as you noted) the skb will be added to tx_queue and left there. If we happen to "ifconfig up" and "rmmod driver" before receiving any packet and before ppp->req_timeout (2 seconds) and before any other PPP interface does the same, we will eventually get skb with invalid ->dev. This is simple to drain in .close (detach is a wrong place since it may be called long after the interface is deactivated, there is no need to delay it past .close). The fix for #1 will already fix #2, but the redundant safety doesn't cost us anything. Thanks for noting the problem, I'll post a patch shortly. Also it seems the timeouts etc. should be configurable. ATM we're only fixing bugs, good. -- Krzysztof Halasa -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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